Spin-lattice relaxation of some less common weakly quadrupolar nuclei

Abstract

Nuclear magnetic spin-lattice relaxation times have been measured for the weakly quadrupolar nuclei 6Li, 9Be, and 133Cs in some simple inorganic and organometallic compounds in isotropic liquid phase. In an attempt to separate the various mechanistic contributions to the total relaxation rate, temperature-dependent T 1 and NOE experiments were performed. For aqueous solutions of the lithium ion extraordinarily long relaxation times were found (up to 1000 sec), with negligible quadrupolar relaxation and with the bulk of the relaxation rate arising from dipolar interactions involving hydrate protons. In systems of lower symmetry, quadrupolar and 6Li 1H dipolar relaxations account for up to 50% of the relaxation rate and the observed relaxation times are typically of the order of tens of seconds. In the hydrated beryllium ion 9Be relaxation is predominantly quadrupolar and dipolar at low temperatures, while spin-rotation prevails at elevated temperatures. In systems of lower beryllium valence electron symmetry the quadrupolar mechanism dominates. In spite of relaxation times of up to 30 sec, 133Cs relaxation in the solvated ionic state appears to be entirely quadrupole dominated.